There is known a compression-vacuum percussive action machine comprising a housing which accommodates a cylinder with a piston, a drive connected to the piston by a crank mechanism, and a hammer connected to the piston by way of an air cushion and engaging with a work tool (cf., DE, B, No. 2,407,879). In order to reduce vibration, the crank has a counterweight. The counterweight is positioned so that the forces of inertia arising as a result of rotation of the crank from the translational movement of the piston and counterweight are oppositely directed. Acting on the housing of the machine in counterphase, these forces balance each other, whereby vibration of the housing of the compression-vacuum machine is reduced. A disadvantage of this machine is high vibration of the housing corresponding to the frequency of movement of the hammer caused by a continuously varying pressure in the air cushion, as the forces caused by the pressure in the air cushion which varying in sign and magnitude are not balanced.
There is also known a compression-vacuum percussive action machine comprising a housing which accommodates a cylinder containing a hammer intended to engage with a work tool, and a piston separated from the hammer by an air cushion and capable of reciprocating inside the cylinder, a crank connected to the piston and linked with a drive by a counterweight whose centre of mass is offset relative to a straight line passing through the points of intersection of the axes of the drive shaft and crank with a plane perpendicular to the axis of the drive shaft (cf., J. E. Ivanov "Povyshenie nadezhnosti kompressionno-vakuumnykh otboinykh elektromolotkov", Ref. sbornik "Mekhanizirovanny instrument i otdelochnye mashiny", vypusk 3, 1967, NIIinfstroidorkommunmash, Moscow, pages 8 and 9).
In this compression-vacuum percussive action machine vibration caused by pressure forces periodically acting axially of the movement of the piston are reduced through compensating such forces by centrifugal forces of the asymmetrical counterweight. Displacement of the counterweight relative to the axis of the crank is such that the centrifugal force arising during rotation of the counterweight is directed in a counterphase to the maximum pressure force in the air cushion. This in turn reduces the action of the pressure forces exerted on the housing and brings down its vibration axially of the machine.
One disadvantage of the above machine resides in excessive vibration of the housing in a direction perpendicular to the travel path of the piston, because, as a rule, the pressure forces in the air cushion prevail over the forces of inertia of the reciprocating piston. Therefore, a counterweight of substantial mass is necessary to compensate for the forces of pressure in the air cushion. The centrifugal force of such a counterweight is not balance in a direction perpendicular to the travel path of the piston, which leads to high vibrations of the housing in this direction.